What Do We Owe the Future? 我們欠未來的人什麼？

🔊A year later Edmund Burke, writing against the same revolution, drew the opposite picture. Society is a contract, he agreed, and it is no ordinary one. It is a partnership in all science, all art, and every virtue, and since its ends cannot be reached in many generations, “it becomes a partnership not only between those who are living, but between those who are living, those who are dead, and those who are to be born.” The living are temporary possessors. They have no right to commit waste on the inheritance and leave to those who come after them “a ruin instead of an habitation.”

一年之後，艾德蒙・柏克在一本反對同一場革命的書裡，畫出了相反的圖像。他同意社會是一份契約；而它並不是一份尋常的契約。它是在一切學問、一切藝術與每一種德行上的合夥；而既然它的目的在許多世代之內都無法達成，「它就成了這樣的一種合夥：不只是活著的人之間的，而是活著的人、已死的人，與將要出生的人之間的。」活著的人是暫時的持有者。他們沒有權利糟蹋這份遺產，留給後來的人「一片廢墟，而不是一個住處」。

🔊The two are usually set against each other, and they share more than they seem to. “Usufruct” is a term of law for the right to use a thing and enjoy its fruits without damaging the thing itself. Jefferson’s living generation may use the earth freely, and may not use it up. Both men hold that we are tenants. They differ on whether the dead may give the tenants instructions.

人們通常把這兩人對立起來；而他們共有的東西，比看起來的多。「用益權」是一個法律用語：使用一樣東西、享用它的收益，卻不損壞那樣東西本身的權利。傑佛遜筆下活著的那一代，可以自由地使用大地；卻不可以把它用光。兩人都主張我們是房客。他們不同的地方在於：死者可不可以對房客下指示。

🔊Three features make the future a hard case. The first is that power runs one way. We can help or hurt people who will live in two hundred years, and they can do nothing for us or to us. Any theory that grounds duties in mutual advantage has nothing to hold on to. Rawls saw the difficulty and placed the parties behind his veil of ignorance without knowledge of which generation they belong to. They would then agree to save for their successors at a rate they would have wanted their predecessors to follow.

有三個特點，使未來成為一個難題。第一，力量是單向的。我們可以幫助或傷害兩百年後活著的人；而他們既不能為我們做什麼，也不能對我們做什麼。任何一個把義務建立在互利之上的理論，在這裡都沒有著力點。羅爾斯看到了這個困難；他讓無知之幕後面的各方，不知道自己屬於哪一個世代。這樣一來，他們會同意為後繼者儲蓄，而儲蓄的比率，就是他們會希望前人遵守的那一個。

🔊The second is that we do not know who they will be or what they will want. This is a reason for modesty about the gifts we choose for them. It does not weaken the case against leaving them poisons, since we can be confident that they will need air, water, soil, and a stable climate. The third feature is the strangest, and it was noticed only in the 1970s.

第二，我們不知道他們會是誰，也不知道他們會想要什麼。這是一個理由，要我們在替他們挑選禮物的時候謙虛一點。它並沒有削弱「不要留毒物給他們」的理由；因為我們可以確信，他們會需要空氣、水、土壤，以及穩定的氣候。第三個特點最奇怪；而且到了 1970 年代才有人注意到。

🔊Suppose a society must choose between two energy policies. One conserves resources, and the other depletes them and gives the people of the next two centuries a slightly easier life, followed by a much worse one. Under depletion, people would hold different jobs, live in different places, and meet different partners. Within a few generations no one would be born who would have been born under the other policy, because each of us comes from a particular pair of cells joined at a particular time. Now consider the people who live badly in the third century of depletion. They cannot say that the policy made them worse off. Had the other policy been chosen, they would never have existed. If their lives are worth living, depletion harmed no one.

假設一個社會必須在兩種能源政策之間選擇。一種保育資源；另一種把資源耗盡，給接下來兩個世紀的人稍微輕鬆一點的生活，接著是糟得多的生活。在耗盡的政策之下，人們會做不同的工作、住在不同的地方、遇到不同的伴侶。幾個世代之內，就不會有任何一個「在另一種政策之下也會出生」的人出生了；因為我們每一個人，都來自在某個特定時刻結合的某一對特定的細胞。現在考慮那些在耗盡政策的第三個世紀裡過得很糟的人。他們不能說，這項政策使他們的處境變差了。如果當初選了另一項政策，他們根本不會存在。只要他們的生命還值得活，耗盡政策就沒有傷害任何人。

🔊Derek Parfit, who set out this non-identity problem in 1984, did not conclude that depletion is acceptable. He concluded that our ordinary idea of wrongdoing, on which an act is wrong only if it is worse for someone, cannot be the whole truth. Some acts are wrong because of the kind of world they bring about, whoever lives in it. He spent years looking for the principle that would say this without leading to conclusions he found repugnant, and said that he had not found it.

德瑞克・帕菲特在 1984 年提出了這個「非同一性問題」；他並沒有結論說耗盡是可以接受的。他的結論是：我們尋常的「做錯事」的觀念，也就是「一個行為只有在對某個人比較糟的時候才是錯的」，不可能是全部的真相。有些行為之所以錯，是因為它們帶來的那種世界；不管住在裡面的是誰。他花了許多年尋找那條原則：能把這一點說出來，又不導向他認為令人反感的結論。他說，他沒有找到。

🔊Governments answer the question every time they weigh a cost today against a benefit later, and they answer it with a number. Economists discount future costs and benefits at a yearly rate, for three reasons that are worth keeping apart. People in the future will probably be richer, so a dollar will mean less to them. The future is uncertain, and the benefit may never arrive. And people simply prefer goods sooner. The third reason, applied to the welfare of other people, has been attacked by economists themselves. Frank Ramsey, who founded the theory in 1928, called it ethically indefensible and said that it arose merely from the weakness of the imagination.

各國政府每一次拿今天的成本去衡量日後的效益，都在回答這個問題；而它們是用一個數字來回答的。經濟學家以一個年率把未來的成本與效益「折現」；理由有三個，值得分開來看。未來的人大概會比較富有，所以一塊錢對他們的意義比較小。未來是不確定的；那份效益也許永遠不會到來。還有，人們就是偏好早一點得到好東西。第三個理由用在別人的福祉上，受到了經濟學家自己的抨擊。法蘭克・拉姆齊在 1928 年奠定了這套理論；他說這種做法在倫理上站不住腳，只是出於想像力的薄弱。

🔊The number matters more than any argument in this lesson. At a rate of three percent, a harm that falls in two hundred years counts for less than one three-hundredth of the same harm today. The dispute over climate policy between the Stern Review of 2006 and its critics was in large part a dispute about this number. At the other extreme stands the view called longtermism, which gives future people the same weight as present ones. Since they may outnumber us by thousands to one, it concludes that shaping the far future is the most important thing we do. Its critics reply that a theory which lets enormous and speculative future benefits outweigh the plain needs of the living poor has gone wrong somewhere.

這個數字，比這一課裡的任何一個論證都更要緊。以百分之三的比率，一項落在兩百年後的傷害，算起來還不到今天同樣傷害的三百分之一。2006 年的《史登報告》與它的批評者之間關於氣候政策的爭論，很大一部分就是關於這個數字的爭論。另一個極端，是稱為「長期主義」的看法：它給未來的人與現在的人同樣的份量。既然他們的人數可能是我們的幾千倍，它的結論是：塑造遙遠的未來，是我們所做的最重要的事。它的批評者回答：一個理論，如果讓龐大而出於推測的未來效益，壓過了活著的窮人明明白白的需要，那它一定在某個地方出了錯。

🔊The Chinese tradition approached the matter through the family and the seasons, and came to it earlier. Mencius told a king that good government begins with restraint in taking: “If close-meshed nets are not allowed in the pools and ponds, there will be more fish and turtles than can be eaten. If axes enter the hills and forests only at the proper time, there will be more timber than can be used.” The rule concerns what a community may take if those who come after are to take as well. The motive given is care for one’s own people. Rights do not come into it.

中國的傳統是透過家族與時令來處理這件事的；而且來得更早。孟子告訴一位國君，好的治理從取用的節制開始：「數罟不入洿池，魚鼈不可勝食也；斧斤以時入山林，材木不可勝用也。」這條規矩講的是：如果後來的人也要能取用，一個群體現在可以取多少。它給出的動機，是對自己人民的照顧。這裡沒有提到權利。

🔊The other side of the bargain is told in the story of the Foolish Old Man. At nearly ninety he begins to dig away the two mountains that block his door. A clever neighbor laughs at him, and he answers: “Though I die, my sons will remain. My sons will have grandsons, and the grandsons will have sons. Sons and grandsons without end, and the mountains grow no higher. Why should they not be leveled?” A person who thinks of himself as one link in a line can begin work that he will not finish and plant trees whose shade he will not sit in. On this view what we owe the future is the reverse side of what we owe the past, and both are paid in the same coin.

這筆交易的另一面，是在愚公的故事裡講的。他年近九十，動手去挖那兩座擋住他家門的山。一個聰明的鄰人嘲笑他；他回答：「雖我之死，有子存焉；子又生孫，孫又生子；子又有子，子又有孫，子子孫孫無窮匱也，而山不加增，何苦而不平？」一個把自己看成一條線上的一環的人，可以開始做他完成不了的工作，可以種下他坐不到樹蔭的樹。照這個看法，我們欠未來的，就是我們欠過去的東西的另一面；而兩者是用同一種錢來還的。